Chapter 3: Acids And Bases

Front 1

Bronsted-Lowry Acid-Base Reactions

Back 1

* Involves the transfer of protons

Front 2

Conjugate Acid

Back 2

* Molecule or ion formed when a base accepts a proton

Front 3

Conjugate Base

Back 3

Molecule or ion that forms when an acid loses its proton

Front 4

Brønsted-Lowry acid

Back 4

a substance that can donate (or lose) a proton.

Front 5

Brønsted-Lowry base

Back 5

* substance that can accept (or remove) a proton

Front 6

Strong Acids

Back 6

* Hydrogen Chloride (HCl)
* Hydrogen Iodide (HI)
* Hydrogen Bromide (HBr)
* Sulfuric Acid (H2SO4)

Front 7

Diprotic Acid

Back 7

* Acid that can transfer 2 protons
* Ex. Sulfuric Acid, first proton transfers completely, while second does not

Front 8

Hydronium Ion

Back 8

* strongest acid that can exist in water to any significant extent
* Any acid stronger than hydronium ion will simply transfer its proton to a water molecule to form hydronium ions
* H3O+

Front 9

Solvated Ions

Back 9

* When an ionic compound dissolves in water

Front 10

Spectator Ion

Back 10

* play no part in the acid-base reaction
* Solvated ions

Front 11

Ionic Reaction

Back 11

* A reaction involving ions as reactants, intermediates, or products. Ionic reactions occur through the heterolysis of covalent bonds.

Front 12

Net Ionic Reaction when Solutions of all Aqueous Strong Acids and Bases are Mixed

Back 12

Front 13

Curved Arrows

Back 13

* Show the direction of electron flow in a reaction mechanism
* Draw the curved arrow so that it points from the source of an electron pair to the atom receiving the pair
* Always show the flow of electrons from a site of higher electron density to a site of lower electron density
* Never use curved arrows to show the movement of atoms. Atoms are assumed to follow the flow of the electrons
* Make sure that the movement of electrons shown by the curved arrow does not violate the octet rule for elements in the second row of the periodic table

Front 14

Lewis acid-base theory

Back 14

* Acids are electron pair acceptors
* Bases are electron pair donors

Front 15

Lewis Acid

Back 15

* Any electron deficient atom can act as a Lewis acid

Front 16

Lewis Acid-Base Reaction of Bromine and Ferric Bromide

Back 16

Front 17

Lewis Acid-Base Reaction of Boron Triflouride and Ammonia

Back 17

* BF3 has substantial positive charge on boron atom
* NH3 has negative charge located at nonbonding pair
* Nonbonding electron fills boron's shell
* Positive charge of product is localized near nitrogen
* Negative charge of product is localized near boron trifluoride

Front 18

Heterolysis

Back 18

* Cleavage of a covalent bond so that one fragment departs with both of the electrons of the bond that joined them
* Normally produces a positive and negative ion

Front 19

Carbocation

Back 19

* Ion with positive charge on carbon atom
* Electron deficient (6 electrons in valence shell)
* Lewis acid
* Short lived and highly reactive
* electrophile

Front 20

Carbanion

Back 20

* Ion with negative charge on carbon atom
* Electron rich
* Have unshared electron pair
* Lewis base
* nucleophile

Front 21

Electrophile

Back 21

* Reagents that seek electrons as to achieve the stable shell configuration of a noble gas
* All Lewis acids are electrophiles
* Atoms that are electron poor due to polarity are electrophiles

Front 22

Nucleophile

Back 22

* Seeks a positive center
* All Lewis bases are nucleophiles

Front 23

Acid strength

Back 23

* The strength of an acid is related to its acidity constant, Ka or to its pKa. The larger the value of its Ka or the smaller the value of its pKa, the stronger is the acid.

Front 24

Acidity Constant (Ka)

Back 24

* If high (greater than 10), acid is a strong acid and if small, the acid is a weak acid

Front 25

pKa

Back 25

* Larger the value, weaker the acid

and the stronger the base

Front 26

pH

Back 26

Front 27

Predicting the Strength of Bases

Back 27

* The stronger the acid, the weaker its conjugate base
* Larger pKa value, the stronger the base
* Amines, like ammonia are weak bases

Front 28

Acid-Base Reactions

Back 28

* Acid-base reactions always favor the formation of the weaker acid and the weaker base
* Increased difference of pKa of acids will more heavily favor the formation of products

Front 29

Carboxylic Acid Solubility as the Result of Salt Formation

Back 29

* Although acetic acid and other carboxylic acids containing fewer than five carbon atoms are soluble in water
* However, insoluble carboxylic acids dissolve in aqueous sodium hydroxide

Front 30

Amine Solubility as the Result of Salt Formation

Back 30

* Amines of low molecular weight are very soluble in water (methylamine)
* Amines of higher molecular weights like aniline are water-insoluable

Front 31

Strength of a Bronsted-Lowry Acid

Back 31

* Depends on extent to which a proton can be separated from it and transferred to a base
* Involes breaking a bond to the proton and making the conjugate base more electrically negative
* Bond strength to the proton decreases as we move down the column of periodic table, increasing its acidity
* Acidity increases from left to right when we compare compounds in a given row of the periodic table, due to increasing stability of conjugate base

Front 32

Electronegativity and Acid Strength

Back 32

* Affects the polarity of the bond to the proton
* Affects relative stability of the anion (conjugate base) that forms when the proton is lost
* Positively correlated with acidity
* Negatively correlated with strength of base

Front 33

Hybridization and Acidity

Back 33

* having more s character means that the electrons of the anion will, on the average, be lower in energy, and the anion will be more stable
* Greater s character, means more acidity
* An sp carbon atom is effectively more electronegative than an sp2 carbon, which in turn is more electronegative than an sp3 carbon
* Opposite is true for base strength

Front 34

Inductive Effects

Back 34

* An intrinsic electron-attracting or -releasing effect that results from a nearby dipole in the molecule and that is transmitted through space and through the bonds of a molecule.
* Effects weaken as distance from the group increases

Front 35

Energy

Back 35

* Energy is the capacity to do work.
* release of heat results from a change from potential energy to kinetic energy in chemical reaction

Front 36

Kinetic Energy

Back 36

* Energy that results from the motion of an object.

Front 37

Potential Energy

Back 37

* Stored Energy

Front 38

Relative Stability

Back 38

* The more potential energy an object has, the less stable it is

Front 39

Potential Energy and Covalent Bonds

Back 39

* release of heat results from a change from potential energy to kinetic energy
* greatest potential energy is the state of free atoms
* formation of a chemical bond is always accompanied by the lowering of the potential energy of the atoms

Front 40

Enthalpy Change

Back 40

* measure of the difference in the total bond energy of the reactants and products.
* Symbolized by Delta H

Front 41

Exothermic Reactions

Back 41

* Negative change in enthalpy
* Evolve heat

Front 42

Endothermic Reactions

Back 42

* Positive change in enthalpy
* Absorbs heat

Front 43

Free Energy Change

Back 43

* Reaction is favored if negative (equilibrium greater than 1)
* Reaction is not favored if positive (equilibrium constant is less than 1)
* For reaction where the number of products equals reactants, entropy is small and therefore change in enthalpy will largely determine favorability of reaction (except at high temps)

Front 44

Acetic Acid vs. Ethanol Acidity

Back 44

* Ethanol is less acidic than acetic acid since it is less favorable to lose an H
* Attributed to conjugate base of acetic acid being more stable

Front 45

Stability of Acetate Ion vs. Ethoxide Ion

Back 45

* Delocalization of charge (as depicted by reasonance structures of carboxylate ion)
* Inductive electron withdrawing effect
* The more stable a conjugate base is, the stronger the corresponding acid

Front 46

Delocalization Effect (by reasonance)

Back 46

* Negative or positive charge is distributed evenly stabilizing charge

Front 47

Inductive Effect - Acetic Acid & Ethanol

Back 47

* Acetate anion's electron-withdrawing effect is distributed amongst O atoms due to reasonance
* Ethanol's anion's electron-withdrawing effect is localized to only 1 O atom
* Acetate Anion is more stable

Front 48

Substituent Effect

Back 48

* greater acidity of chloroacetic acid can be attributed, in part, to the extra electron-attracting inductive effect of the electronegative chlorine atom
* also stabilizes the chloroacetate ion that is formed when the proton is lost by dispersing its negative charge
* any factor that stabilizes the conjugate base of an acid increases the strength of the acid

Front 49

Halogen Elements

Back 49

Fluorine (F); Chlorine (Cl); Bromine (Br); Iodine (I); Astatine (At)

Front 50

Acetone

Back 50

- simplest Ketone

- (CH3)2CO

Front 51

Acetaldehyde

Back 51

- CH3CHO

Front 52

Protic Solvent

Back 52

* Contains a H atom attached to a strongly electronegative element such as O or N
* can form hydrogen bonds to the unshared electron pairs of an acid and its conjugate base, but they may not stabilize both equally

Front 53

Acidity in the Gas State

Back 53

* In the absence of a solvent (i.e. in the gas phase) most acids are weaker than in a solution
* Ions formed in a acid-base reaction are oppositely charged and must be separated
* Separation is difficult in the gas state

Front 54

The Effect of the Solvent on Acidity

Back 54

* The stability of a conjugate base is enhanced if it is solvated to a greater extent than the corresponding acid.
* Relative acidity cannot be predicted solely on the basis of solvation

Front 55

Pronated alcohol

Back 55

* Conjugate acid of the alcohol

Front 56

Alkyloxonium Ion

Back 56

An alcohol with an oxygen with a formal positive charge

Front 57

Dialkyloxonium Ion

Back 57

* An ether containing an O with a positive formal charge

Front 58

Protonated Ketone

Back 58

* Compounds containing a carbonyl group also act as bases in the presence of strong acid

Front 59

Substitution Reaction

Back 59

* A reaction in which one group replaces another in a molecule.

Front 60

Reaction of tert-Butyl Alcohol with Concentrated Aqueous HCl

Back 60

* Step 2 occurs because alcohol is protonated, positive charge on O weakens C-O bond
* why doesn't a molecule of water (also a Lewis base) instead of a chloride ion react with the carbocation in step 3? (3.12)

Front 61

Leveling Effect of Solvent

Back 61

* An effect that restricts the use of certain solvents with strong acids and bases.
* no acid stronger than the conjugate acid of a particular solvent can exist to an appreciable extent in that solvent
* no base stronger than the conjugate base of the solvent can exist to an appreciable extent in that solvent.

Front 62

Alcohols as Solvents

Back 62

* Often used for organic reactions
* Less polar than water, so dissolve less polar compounds
* Offers advantage of using alkoxide ions (RO-) as bases (stronger base than hydroxide ions)

Front 63

Alkyllithium

Back 63

* RLi
* Although has covalent character, it is polarized to make C negative
* Reacts as though it contains alkanide ions

Front 64

Alkanide ions

Back 64

* Conjugate bases of alkanes
* Strongest bases

Front 65

Terminal Alkynes

Back 65

* alkynes with a proton attached to a triply bonded carbon
* Have a pKa of about 25
* React with sodium amide in liquid ammonia

Front 66

Deuterium

Back 66

* Isotope of hydrogen
* 2 amu

Front 67

Tritium

Back 67

* Isotope of hydrogen
* 3 amu

Front 68

Duetrium and Tritium Labeled Compounds

Back 68

* Duetrium or tritium replace 1 or more H atoms of a compound
* A means to label or identify paticular H atoms
* One ethod: very strong base is treated with D2O or T2O